Posting order for a nine-tile grid

Nine files, nine uploads, and exactly one sequence that produces the picture you cut. Get it wrong and the grid is mirrored through its own diagonal, which is not something you can fix by rearranging anything afterwards.

Why the last tile is posted first

A profile lists posts newest first, filling from the top left and pushing everything else along and down. That means the top-left cell always holds whatever was posted most recently. A grid is therefore assembled in reverse: the tile that belongs at the bottom right is the oldest post in the set, so it goes up first, and the tile that belongs at the top left is the newest, so it goes up last.

Written out for a 3 × 3, where r1c1 is the top-left tile of the original picture, the upload sequence is:

r3c3, then r3c2, then r3c1 — the bottom row, right to left.
r2c3, r2c2, r2c1 — the middle row, right to left.
r1c3, r1c2, r1c1 — the top row, right to left, finishing at the top-left tile.

The archive this tool produces carries that list as posting-order.txt with every tile’s pixel size next to it, and the preview prints the same number on each tile. It is worth checking the first two uploads against the list rather than trusting a mental model of the order; the sequence is easy to state and surprisingly easy to invert under pressure.

Posting a grid across several days

Nothing about the sequence changes if you spread it out. What changes is the risk, because the grid is only intact as long as nothing else is posted between the first tile and the last. One unrelated post in the middle of the run shifts every tile after it by one cell and the picture breaks in a way that looks like a cutting error and is not.

If you have to post something else

Finish the grid first, or wait. There is no ordering trick that lets an unrelated post sit inside a grid run without moving it, because the grid’s layout is simply the post list reflowed into three columns.

If the grid is longer than three rows

A 3 × 4 is twelve uploads and a 3 × 5 is fifteen. The arithmetic is identical and the exposure is longer, which is the real argument for cutting a 3 × 3 the first time you try this.

Recovering a grid that is half built

The recoverable cases are narrower than most people expect, and it is worth knowing which one you are in before you start deleting things.

Posted in the wrong direction, nothing else in between: delete the lot and re-upload in the right order. The tiles themselves are fine; only the sequence was wrong.
Right order, but something unrelated landed in the middle: deleting the intruder closes the gap and the grid reassembles. Deleting a tile instead does not.
Some tiles posted, then a long pause: carry on from where you stopped, in the same direction. A pause costs nothing as long as nothing was posted during it.
Tiles posted at different crops or from different exports: re-cut from the original and start again. Mixed sources never line up, because the framing decision was made twice.

Keep the archive until the grid is finished. Re-cutting from the original picture is cheap; reconstructing which crop produced which tile a week later is not.

When this stops being true

Everything above rests on one platform behaviour: newest post top left, three columns, filling left to right. That is a layout decision made by somebody else and it has changed before on other products.

If the fill direction ever changes, every posting order on this site and inside every archive it has produced becomes wrong on the same day, and the tiles stay correct. Check the first two uploads against the live profile before committing to the remaining seven — that check costs a minute and is the only one that does not depend on this page being current.